http://www.kentonline.co.uk/medway/sport/gills-left-back-choice-explained-31189/
Doug Loft played at left back because the four man coaching staff wanted some experience in the back four.
I personally thought that Doug Loft struggled at left back through-out the entire game against Walsall and at least when Bradley Garmston came on, Gillingham had a left back playing at left back, although I do think that Bradley Garmston looks like a attacking winger who is being asked to play as a full back because his defensive qualities are not as good as his attacking ability.